Office chair

ABSTRACT

A chair with a reclining system that allows the back and seat to recline at different angles. The chair is provided with a first member, a second member, and a third member. The first member is pivotally attached to the second member and the third member, while the second member and the third member are pivotally and slidably attached together. The second member comprises an axle, which extends across the width of the third member, that is installed into open slots in the third member, thereby providing the pivotal and slidable connection. Assist springs and a height adjustment system is also provided.

FIELD OF THE INVENTION

[0001] The present invention relates generally to chairs, and moreparticularly, to a reclining system for the seat and back and a heightadjustment mechanism for the seat.

BACKGROUND

[0002] An office chair is a well-known piece of furniture that allows auser to comfortably sit in the chair while performing various worktasks. Manufacturers of office chairs have always faced a difficult taskwhen trying to produce an office chair that will be suitable for a broadvariety of different people. One reason for this difficulty is thatusers of chairs vary greatly in their relative size and proportions. Theheights of users, for example, can vary significantly, with some usersbeing taller while others are shorter, and some users having longertrunk proportions while others have longer leg sections. In addition,the size of users varies, with some being larger while others aresmaller. Another difficulty that manufacturers must consider is the widevariety of tasks that different users perform in their office chairs.Although many users perform similar tasks in their chair like working ona computer, writing at a desk, or reading documents, the workenvironment and the type of individual user can vary greatly. Forexample, the tasks performed while sitting in a chair can differconsiderably between workers in a factory, a home-office, or at anadministration center. Different types of users, like executive workersand staff workers, also have different requirements for their chair.

[0003] Notwithstanding these difficulties, the most difficult issue thatmanufacturers must confront is the various preferences of individualusers. Seldom do the individual preferences of different users coincideexactly. Often a user will generate strong personal opinions about anoffice chair as a result of the long periods of time in which the usersits in the chair and the direct intimate contact that the user has withthe chair. To a large extent, manufacturers have been forced to addressthis wide range of personal preference by providing many different chairdesigns so that different users can choose a chair that satisfies theirparticular preferences. At the same time, manufacturers strive fordesigns which are cost effective to produce and which will satisfy asmany users as possible.

[0004] One preference that all users share is a desire for an officechair that is comfortable. One feature that chair manufacturers ofteninclude to make a chair more comfortable is a tilt mechanism. Thismechanism allows the back of the chair to recline rearward when the userapplies pressure with his upper body to the back of the chair. Thisallows the user to relax in a more laid back, fully supported position.Typically, a range of about 20° of rearward travel is commonly provided,with a constant amount of pressure required to recline the backthroughout the travel range.

[0005] One reclining system that is commonly used for office chairsinvolves a single pivot between the stem of the chair and the seat andback assembly. Typically, the pivot is located beneath the seat andbehind the front edge of the seat. In this system, the seat and the backare rigidly attached to each other so that the back is orientedapproximately 90° in a vertical direction from the seat. A spring isthen provided to bias the seat and back assembly forward into anunreclined position in which the seat is approximately horizontal to thefloor and the back is approximately vertical. When the user appliespressure to the back of the chair, the pivot and spring allow the seatand the back to rotate rearwardly together around the pivot. Some usersfind this reclining system undesirable, however, because of the rigidattachment of the seat and the back. One especially undesirable resultof this reclining system is that the front edge of the seat moves upwardas the back is reclined. Because the seat and the back are rigidlyattached to each other, the rotating movement of the seat and backassembly around the pivot causes the front edge of the seat to moveupwards from its unreclined position. This upward movement placespressure on the underside of the user's legs and can lift the user'slegs slightly off the floor.

[0006] To resolve this problem of seat movement during reclining, otherchairs provide a fixed placement of the seat. The back is then reclinedrearward independently of the seat. These systems, however, producefriction and pulling between the back of the chair and the user's upperbody because the back generally travels along a different angularrotation than the user's upper body. As a result, the user usually feelsan upward pulling on his clothes as he reclines.

[0007] A more desirable reclining system allows the seat to move duringreclining, but at a different rate of travel than the back. Onechallenge in designing these types of reclining systems is achieving anoptimal balance between the seat movement and back travel duringreclining. The system must also be cost effective and simple tomanufacture. One desirable way to reduce the cost of a reclining systemis to minimize the number of parts that are required in the assembly. Inaddition, another way to reduce costs is to design the reclining systemso that it is easy to assemble. This ease of assembly has becomeincreasingly important recently as chair manufacturers have begun toship chairs unassembled directly to end users. Thus, the recliningsystem should be capable of being assembled without needing numerousspecial tools. Finally, the reclining system must be durable so that itcan survive over a long lifetime without failure in a variety of workenvironments.

[0008] One problem with some reclining systems is that the leverageapplied to the main spring changes as the back is reclined rearward. Forexample, in some systems a greater amount of leverage is applied whenthe back is reclined rearward than when the back is upright. Thisresults in the user feeling less support from the back the further theuser reclines rearward. To compensate for this characteristic, somechairs have provided assist springs to supplement the reclining pressureprovided by the main spring. The assist springs, however, must be costeffective and simple to install. Desirably, the assist springs can beintegrated into the reclining system without a significant number ofspecial features required to add the assist springs.

[0009] Another feature that manufacturers commonly provide on officechairs to improve comfort is a height adjustment system for the seat andthe back. This feature is especially important because the length ofdifferent users' legs varies greatly. Generally, users prefer to adjustthe height of their chair so that their feet rest flat on the floor andtheir upper legs are parallel to the seat. Often, however, a chair isused by a variety of different people, who each have their own preferredheight for the seat. This is especially true of chairs that are sharedby many people, such as conference room chairs. Because the height ofthese chairs must be changed frequently by many different people, theadjustment system should be capable of being changed quickly withoutrequiring time consuming adjustments. The height adjustment systemshould also be simple to operate so that temporary users will be able toquickly learn how to change the height of the seat without becomingconfused.

[0010] Commonly, office chairs have included adjustable cylinders in thestem of the chair to provide the desired height adjustment. Thesecylinders generally employ a valve stem that is oriented horizontally,or parallel, to the floor. Thus, in order to release the cylinder toallow the height of the chair to be adjusted, an actuating system isprovided that actuates the horizontal valve stem upward and downward.However, in these systems the vertical positioning of the actuatingsystem in relation to the horizontal valve stem is usually quitecritical. This typically makes the manufacturing and assembly of theheight adjustment system more expensive and complicated. The manner ofusing these systems can also become complicated, thus confusing the useras he attempts to adjust the height of the chair.

[0011] Generally, reclining systems provide the desired recliningpressure to the back with a spring that is increasingly stressed as theback is reclined rearward. Because individual users commonly preferdifferent amounts of reclining pressure, manufacturers typically providea spring adjustment system that can be used by the user to increase ordecrease the amount of reclining pressure. The spring adjustment systemusually includes a screw that can be turned by the user, thereby movinga spring guide that increases or decreases stress in the spring.Generally, manufacturers install the spring into the reclining systemwith a small amount of initial stress introduced into the spring whenthe adjusting screw is turned to the lowest pressure setting. Therefore,the user is prevented from relieving the entire stress in the springwhen the adjusting screw is turned. This preload stress is desirablebecause an unstressed spring will tend to rattle in the reclining systemwhen the chair is moved about. The back of the chair will also be looseand will flop in the upright position between the forward stop and thespring. In addition to these problems, some spring adjustment systemsrequire a minimum amount of spring pressure at all times in order tofunction properly.

[0012] Typically, manufacturers introduce the preload stress into thespring either manually or with special tools while the spring is beinginstalled into the reclining system. Thus, in the case of some springassemblies, a force as high as 100 lbs may need to be applied tocompress the spring during installation. This combined procedure ofcompressing the spring while simultaneously installing the spring intothe reclining system can become quite difficult and time consuming. Thisprocedure is also undesirable for chairs that are shipped unassembleddirectly to end users who may not have the special tools necessary toinstall the spring with the necessary preload stress. Thus, a system foreasily introducing an initial preload stress into the spring isdesirable.

[0013] To provide further comfort for the user, manufacturers oftenprovide arm rests on the chair so that the user can conveniently resthis forearms. Other users, however, prefer not to have arm rests ontheir chairs because the arm rests can obstruct the sides of the chairand can interfere with free movement into or out of the chair. Chairswithout arm rests are also preferred to save costs when the chair willbe used infrequently.

[0014] Thus, a modular arm rest system is desirable to allow chairs tobe provided with or without arm rests. Desirably, this system wouldinclude a reclining chair and a four-legged stacker chair. A modular armrest system such as this could increase the number of chairconfigurations possible and could minimize costs by using commoncomponents or components with similar functions. The arm rest system,however, must provide a rigid, secure attachment to the chair frame inorder to satisfy the user's expectations of quality. In addition, thearm rest system should be simple and easy to install to allow users toinstall or remove the arm rests themselves. Finally, an arm rest systemthat allows users to reconfigure a chair later after initial assembly ofthe chair would be preferred.

[0015] One area of the chair that has a significant impact on a user'ssatisfaction with the chair is the seat. The seat is the surface uponwhich the user rests his buttocks, and as such, the seat directlyinfluences the overall comfort of the chair. Generally, users prefer aseat that is soft, yet supportive. In addition, seats that provideincreased aeration through the seat surface tend to be more comfortable.

[0016] One type of seat that has been used is a fabric seat that issupported around the circumference by a seat frame. In this type ofseat, the fabric is a membrane designed to provide increased aeration.Typically, these seats have been manufactured in an integrated moldingoperation, in which the outer edges of the fabric are secured to theseat frame by being molded into the seat frame. However, thismanufacturing technique can be expensive and requires specialmanufacturing equipment that is not always readily available. Thus, alow cost fabric seat is desirable.

SUMMARY

[0017] Accordingly, a chair is provided with a reclining system, whichincludes a first, second, and third member. The first member ispivotally attached to the second and third members and the second andthird members are pivotally and slidably attached together. To provideeasier assembly and greater durability, the second member includes anintegral axle that extends across the width of the third member. Theaxle is installed into slots in the third member that are open at oneend, thereby providing the pivotal and slidable connection. Preferably,a fourth member is also provided that is pivotally attached to the axleof the second member and which slides within the slots in the thirdmember. The fourth member can also include an integral spring guide.

[0018] Assist springs are also provided in order to provide increasedreclining pressure as the back is reclined. The assist springs areinstalled within the slots in the third member and are compressedbetween the non-moving back face of the slot and a moving face of thefourth member when the back is partially reclined. Preferably, a specialmount is provided to properly orient the springs within the slot. Thespecial mounts also make installation of the springs easier.

[0019] A cost effective height adjustment system is also provided thatmakes adjustments to the height of the chair quick and simple. Theheight adjustment system includes an actuating member that forces avertically oriented valve pin to one side, thereby releasing anadjustable cylinder. A user adjusts the height of the chair by pressinga button on an actuating stem. The actuating stem then forces theactuating member to the side, thus releasing the cylinder. One advantageof this system is that the vertical positioning of the actuating systemand the valve stem is not as critical as traditional systems.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0020] The invention, including its construction and method ofoperation, is illustrated more or less diagrammatically in the drawings,in which:

[0021]FIG. 1 is a perspective view of a task chair, showing a set oftask chair arm rests installed and a fabric seat installed;

[0022]FIG. 2 is a perspective view of a frame assembly;

[0023]FIG. 3 is a perspective view of the frame assembly;

[0024]FIG. 4 is a side elevational view of the frame, showing the hiddeninternal components;

[0025]FIG. 5 is a perspective view of the frame assembly, showing anassist spring;

[0026]FIG. 6 is a perspective view of a bearing guide, showing a mountfor the assist spring;

[0027]FIG. 6a is a perspective view of the bearing guide, showing theassist spring attached to the mount;

[0028]FIG. 7 is a perspective view of the assist spring;

[0029]FIG. 8 is a perspective view of a height adjustment mechanism;

[0030]FIG. 9 is a perspective view of the height adjustment mechanism,with an actuating member and an actuating stem excluded to show a valvestem;

[0031]FIG. 10 is a perspective view of the actuating member;

[0032]FIG. 11 is a cross-sectional view of the height adjustmentmechanism;

[0033]FIG. 12 is a cross-sectional view of a spring preload system,showing a spring guide adjusted to its rear-most position;

[0034]FIG. 12a is a cross-sectional view of the spring preload system,showing the spring guide adjusted forward of its rear-most position;

[0035]FIG. 13 is a perspective view of the spring preload system;

[0036]FIG. 14 is a perspective view of a preload member attached to acover;

[0037]FIG. 15 is a perspective view of a back, showing the top side of ahole for an arm rest;

[0038]FIG. 16 is a perspective view of the back, showing the bottom sideof the hole for an arm rest;

[0039]FIG. 17 is a side elevational view of the task chair, showing atask chair arm rest installed;

[0040]FIG. 18 is a perspective view of the task chair arm rest, showinga connecting member;

[0041]FIG. 20 is a perspective view of the task chair yoke, showing aninterior cavity;

[0042]FIG. 21 is a side elevational view of a set screw;

[0043]FIG. 22 is a perspective view of a task chair, showing task chairplugs installed;

[0044]FIG. 23 is a side elevational view of the task chair plug;

[0045]FIG. 24 is a front elevational view of the task chair plug;

[0046]FIG. 25 is a perspective view of a stacker chair, showing a set ofstacker chair arm rests installed and a fabric seat installed;

[0047]FIG. 26 is a side elevational view of the stacker chair, showingthe stacker chair arm rest installed;

[0048]FIG. 27 is a side elevational view of the stacker chair arm rest,showing a connecting member;

[0049]FIG. 28 is a back elevational view of the stacker chair arm rest,showing the connecting member;

[0050]FIG. 29 is a perspective view of the stacker chair frame, showingan interior cavity;

[0051]FIG. 30 is a side elevational view of a detent assembly having arounded nose;

[0052]FIG. 31 is a side elevational view of a detent assembly having anangled nose;

[0053]FIG. 32 is a perspective view of a stacker chair, showing stackerchair plugs installed;

[0054]FIG. 33 is a side elevational view of the stacker chair plug;

[0055]FIG. 34 is a front elevational view of the stacker chair plug;

[0056]FIG. 35 is a perspective view of a seat frame, showing the topside of the seat frame;

[0057]FIG. 36 is a cross-sectional view of a portion of the seat frame,showing a tooth;

[0058]FIG. 37 is a front elevational view of a portion of the seatframe, showing the tooth;

[0059]FIG. 38 is a top plan view of a portion of the seat frame, showingthe tooth;

[0060]FIG. 39 is a perspective view of the seat frame, showing thebottom side of the seat frame;

[0061]FIG. 40 is a perspective view of a cover, showing the top side ofthe cover;

[0062]FIG. 41 is a perspective view of the cover, showing the bottomside of the cover;

[0063]FIG. 43 is a perspective view of a clip;

[0064]FIG. 44 is a perspective view of a portion of a seat, showing aretention slot in the bottom side of the seat frame;

[0065]FIG. 45 is a perspective view of a portion of the seat, showing apin installed in the retention slot;

[0066]FIG. 46 is a side elevational view of the seat installed onto achair frame, showing the pin installed through a hole in the chair frameand a tinnerman nut installed on the bottom end of the pin;

[0067]FIG. 47 is a top plan view of a machine for installing the fabriconto the seat frame;

[0068]FIG. 49 is a top plan view of a portion of the machine, showingthe seat frame installed on a support and the fabric engaged by a set offront and rear clamps and a set of side clamps;

[0069]FIG. 50 is a cross-sectional view of a portion of the machine,showing a pressing member above the fabric and the seat frame below thefabric;

[0070]FIG. 51 is a cross-sectional view of a portion of the machine,showing the seat frame raised so that the pressing member is within arecessed channel;

[0071]FIG. 52 is a cross-sectional view of a portion of the machine,showing the seat frame and the pressing member raised and the outsideedge of the fabric pulled down around the circumference of the seatframe; and

[0072]FIG. 53 is a cross-sectional view of a portion of the machine,showing the pressing member raised away from the seat frame and the seatframe reciprocated into the fabric.

DETAILED DESCRIPTION Reclining System

[0073] Turning now to the drawings, and particularly to FIG. 1, there isshown an office chair 10. A user sits in the office chair 10 by restinghis upper legs and buttocks on the seat 12 of the chair 10. Although avariety of different seats can be used, a seat 12 like that disclosedbelow can be used. The user's legs extend down along the front of thechair 10 so that his feet are flat on the floor. In order to rest theuser's upper body, the user can lean rearward and relax the back side ofhis upper body against the back 14 of the chair 10. Arm rests 210 arealso provided so that the user can relax his arms on top of the armrests 210. Although arm rests are not needed, and many styles of armrests can be used, arm rests 210 like those disclosed below can be used.The seat 12 is supported along its underside by a chair stem assembly18, and stability is provided by a number of legs 20 that rest on thefloor. Casters 22 are provided on the bottom of the legs 20 to allow thechair 10 to be easily moved from place to place. Flat floor pads,however, could also be used in place of the casters 22.

[0074] Turning now to FIG. 2 through 4, the frame assembly 30 of thechair 10 is a multi-member linkage 30 that allows the back 14 and theseat 12 to recline at different angles. Accordingly, a yoke 32, or firstmember 32, is provided, which is rigidly attached to the back 14. Theyoke 32 extends downward from the back 14 and below the seat 12. Alongthe bottom side of the yoke 32, two extended arms 33 are rigidlyattached to the yoke 32. The extended arms 33 pivotally attach B theyoke 32 to the base 36, or third member 36, along the rear end of thebase 36. The yoke 32 is pivotally attached A to the seat support 34, orsecond member 34, which is rigidly attached to the seat. Along the frontside of the seat support 34, the seat support 34 is pivotally mounted Cthrough an axle 37 to the bearing guide 38, or fourth member 38. Theaxle 37 is an integral portion of the seat support 34 and extends acrossthe width of the base 36. The bearing guide 38 is slidably connected tothe base 36 through a fore-aft slot 40, or pocket 40, in the base 36. Toease assembly, the slot 40 is open at the forward end to receive thebearing guide 38 and the axle 37.

[0075] This multi-member linkage 30, therefore, results in a seat travelthat is different than the reclining angle of the back 14. It can beseen from FIG. 4 that as the back 14 is reclined rearward, the pivotconnection A between the yoke 32 and the seat support 34 will movedownwards. At the same time the front end 35 of the seat support 34 willremain at approximately the same height while moving rearward along thebearing guide slot 40. The rearward movement of the bearing guide 38correspondingly forces the front spring guide 42 rearward, whichcompresses the main spring 46 and provides the desired recliningpressure. Various main springs are possible, but the preferredembodiment includes a spring with a spring rate of 310 lb/in. Thereclining angle is restricted between an upright position and a reclinedposition by two stops 48 that are rigidly attached to the bottom side ofthe yoke 32. The stops 48 extend into slots 50 in the rear end of thebase 36. Thus, when no pressure is exerted by the user against the back14, the main spring 46 forces the yoke 32 forward through the seatsupport 34, and the stops 48 limit this forward movement by abuttingagainst the top side 51 of the slots 50. On the other hand, when theuser exerts full pressure on the back 14, the yoke 32 will rotaterearward compressing the main spring 46 until the stops 48 abut againstthe bottom side 32 of the slots 50.

[0076] Turning now also to FIGS. 5, 6a, and 7, assist springs 54 havebeen provided to increase the reclining pressure as the back 14 isreclined rearward. The assist springs 54 compensate for the increasedleverage that is exerted on the main spring 46 as the back 14 isreclined at higher angles. One characteristic of the multi-memberlinkage 30 previously described is that the linkage 30 displaces themain spring 46 a decreasing amount the further rearward the back isreclined. Thus, the user will feel less resistance, or support, from theback 14 the further rearward the user reclines. However, many usersprefer a more constant amount of support. The assist springs 54,therefore, improve this characteristic of the multimember linkage 30 byengaging at an intermediate position, or about halfway, between theupright and reclined positions of the back 14, thereby providingincreased resistance to further rearward reclining of the back 14.

[0077] The assist springs 54 are mounted within the pockets 40 that areformed in the base 36 for the slidable connection D between the bearingguide 38 and the base 36. Thus, as the bearing guide 38 moves rearwardduring reclining of the back 14, the springs 54 will contact the backface 56 of the pocket 40 and will begin to compress between the backface 56 and the bearing guide 38. Various assist springs are possiblebut the preferred embodiment includes two assist springs with a springrate of 106 lb/in each. Accordingly, as the user reclines the back 14rearward from the upright position towards the reclined position, theuser will feel increased resistance from the assist springs 54 when thesprings 54 engage intermediately, or approximately halfway, through thetotal allowed reclining angle.

[0078] The assist springs 54 are mounted to the back side of the bearingguide 38 onto specially formed mounts 58. Each of the mounts 58 have anouter diameter 59 which fits snugly within the inner diameter 53 of thespring 54 to stabilize the spring 54 in the proper orientation. A rampedtab 60 is also provided inside the outer diameter 59 with an undercutarea 61 in order to retain the spring 54 on the mount 58. Thus, onceinstalled on the mount 58, the bent inward end 55 of the spring 54 willlodge under the ramped tab 60 and will become trapped by the undercutarea 61 below the tab 60. The mount 58, therefore, securely attaches oneend 55 of the spring 54 to the bearing guide 38, leaving the other endof the spring 54 free to abut up against the backside 56 of the pocket40 during reclining. The ramped tab 60 and undercut area 61 also allowthe spring 54 to be easily installed in place during manufacturing. Inorder to install the spring 54, the spring 54 can be simply pushed ontothe mount 58. The bent inward end 55 of the spring 54 will then ridealong the ramped portion of the tab 60 until the bent end 55 reaches theundercut area 61, where it will pop into place.

[0079] In order to prevent the user from pinching fingers, clothing, orthe like within the moving parts of the chair 10 during reclining, apinch guard 62 has been provided to cover the pockets 40 in the base 36.The pinch guard 62 also improves the appearance of the chair 10 bycovering up the unsightly pockets 40 and the internal mechanisms of thechair 10. The pinch guards 62 are attached to the bearing guide 38 andrest flat against the outer sides of the base 36. Thus, when the bearingguide 38 moves rearward during reclining, the pinch guards 62 will moverearward also. The pockets 40 on the base 36, therefore, are alwayscovered, preventing anything from becoming pinched between therearwardly moving bearing guide 38 and the back side 56 of the pockets40. The pinch guards 62 also cooperate with the inner lateral guides 64to laterally retain the bearing guide 38 in place.

[0080] Turning now also to FIGS. 8 through 11, the reclining pressure ofthe back 14 is also adjustable in order to satisfy the individualpreferences of different users. Thus, by adjusting the amount of preloadin the main spring 46, the user can individually set the amount ofreclining pressure that will be exerted when the back 14 is reclinedrearward. The preload on the main spring 46 is adjusted by the user byturning the pressure adjustment knob 66 either clockwise or counterclockwise, depending on whether more or less reclining pressure isdesired. The rotation of the pressure adjustment knob 66 is thentranslated by a spiral bevel gear set 68 to rotate the spring adjustmentscrew 70. The spring adjustment screw 70, however, is fixed in place bya rear shoulder 72 on the spiral bevel gear 68 and a front shoulder 73on the screw 70 so that the screw 70 is prevented from translatingrearward or forward. The screw 70 rotates about a bushing 74 with aTeflon impregnated mesh interior. A thrust surface is also providedbetween a Teflon impregnated lip 75 on the bushing 74 and a washer 76positioned between the lip 75 and the forward shoulder 73. Thus, whenthe pressure adjustment knob 66 is rotated by the user and the screw 70correspondingly rotates, the rear spring guard 44 will travel forward orrearward depending on the rotational direction of the screw 70.Therefore, the initial compression of the main spring 46, or preload,will vary depending on the user's adjustment of the pressure adjustmentknob 66. To ensure a minimum amount of preload in the spring 46 and toease assembly of the pressure adjustment mechanism, a spring preloaddevice like that disclosed below can be provided.

[0081] A height adjustment mechanism 78 is also provided which can beintegrated into the pressure adjustment knob 66. The height adjustmentmechanism 78 allows the user to quickly and easily adjust the height ofthe seat 12 and back 14 depending on the individual preference of theuser. The height adjustment mechanism 78 includes an actuating stem 80installed through the pressure adjustment knob 66. The outer end of theactivating stem 80 forms a button 82 which can be easily depressed bythe user. A spring 83 installed behind the button 82 forces the button82 outward when it is not depressed. The inner end of the actuating stem80 forms a smaller diameter nose portion 84 and a larger diametershoulder portion 85.

[0082] The nose portion 84 of the actuating stem 80 is then installedthrough a slot 88 that extends through the upper portion of theactuating member 86. The actuating stem 80 resists the outward pressureof the spring 83 with a groove 87 located between the nose portion 84and the shoulder 85 that is installed into a retention snap 91 withinthe actuating member slot 88. The actuating member 86 includes afunnel-like cavity 90 along its lower end that is adapted to fit overthe valve pin 96 of the variable height cylinder 97. The actuatingmember 86 also includes a similar funnel-like shape along its exterior92, with the lower outer diameter 94 being approximately the size of theinner cavity surface 98 of the chair stem assembly 18.

[0083] The cylinder 97 is a typical cylinder 97 used by office chairmanufacturers to provide variable height adjustment. A cylinder with alateral release system like that manufactured by Suspa is an example ofone such cylinder. The cylinder 97 is unlocked from its selected heightby pressing the valve pin 96 to the side, which then allows the cylinder97 to freely travel upward and downward. The user, therefore, is able toeasily adjust the height of the chair 10 by depressing the button 82 ofthe actuating stem 80. The shoulder 85 on the other end of the actuatingstem 80 then abuts against the outer sides 89 of the slot 88 in theactuating member 86. This forces the top side of the actuating member 86to pivot around the opposite side of the bottom, flared outer diameter94 of the actuating member 86 when the outer diameter 94 abuts againstthe inner cavity surface 98 of the chair stem assembly 18. As a result,the valve pin 96 is forced to the side by the inner cavity 90 of theactuating member 86, thereby releasing the cylinder 97 to move upward ordownward. When the user releases the button 82 of the actuating stem 80,the actuating member 86 and the valve pin 96 will return to theircentralized position without the need for a separate return device. Thecylinder 97 will then be locked in place at the desired height. Theactuating member 86 also makes the height adjustment mechanism 78 easierto assemble in manufacturing because the vertical placement of thecylinder 97 is less crucial then it is in traditional height adjustmentmechanisms.

Spring Preload System

[0084] Referring now to FIGS. 12, 12a, 13, and 14, a preload system 120is provided in order to eliminate looseness in the main spring assembly122 when the rear spring guide 44 is adjusted to its rear-most position.Looseness in the main spring assembly 122 can result in a rattling ofthe reclining system 30 when the chair 10 is moved about during normaluse. Naturally, user's of the office chair 10 find this rattling noiseto be distracting and disturbing. Typically, this looseness is preventedby introducing an initial compression into the main spring 46 so thatthe spring 46 is always compressed even when the pressure adjustmentknob 66 is turned all the way towards the lowest pressure setting.

[0085] Introducing this initial compression into the main spring 46 canmake installation of the spring assembly 122 quite difficult, however.For example, in the preferred embodiment the main spring 46 has a springrate of 310 lb/in. The desired amount of initial compression in thespring 46 is about 0.090 inch to adequately prevent rattling of thereclining system 30. Therefore, about 28 lbs of force (310 lb/in*0.090in) must be applied to the spring 46 in order to compress itsufficiently to permit installation of the spring 46 into the springassembly 122. As a result, installation of the spring 46 becomesdifficult because of the large amount of force that must be applied tothe spring 46 at the same time that the multiple pieces of the springassembly 122 are being fitted together. This can make manualinstallation of the spring 46 difficult to perform repeatedly in amanufacturing assembly line. Thus, special tools are usually required.These tools, however, can become overly complicated and can make theinstallation procedure more time consuming.

[0086] The preload system 120 alleviates this difficulty by allowing themain spring 46 to be installed without applying any initial compressionto the spring 46. The initial compression is then introduced into thespring 46 after the entire reclining system 30 has been assembled simplyby turning the pressure adjustment knob 66. Thus, the main spring 46 canbe installed by easily fitting together the pieces of the springassembly 122 without applying any force to the spring 46. Although thepreload system 120 can be used on other reclining systems, the preferredembodiment includes a multi-member reclining system 30 like the onedescribed above.

[0087] The spring assembly 122 includes a front spring guide 42 and arear spring guide 44 which entrap and hold the main spring 46 in place.The front spring guide 42 is integrally formed into the bearing guide38. Thus, when the back 14 is reclined rearwardly the forward end of thespring 46 travels rearward along with the bearing guide 38. The rearspring guide 44 is threaded onto the spring adjustment screw 70 and isfixed in place during normal reclining of the chair 10. Accordingly,when the back 14 is reclined, the main spring 46 becomes increasinglycompressed between the rearward moving front spring guide 42 and thefixed rear spring guide 44. As a result, the user feels a supportiveresistance from the back 14 as the user presses rearwardly against theback 14.

[0088] The resistance that the user feels from the back 14 duringreclining can be adjusted by turning the pressure adjustment knob 66 ineither a clockwise or counter-clockwise direction for increased ordecreased resistance, respectively. When the pressure adjustment knob 66is turned, the spiral bevel gear set 68 is engaged and the springadjustment screw 70 rotates correspondingly. However, the rear springguide 44 is prevented from rotating due to the pressure applied to therear spring guide 44 by the mainspring 46 and the resulting frictionbetween the guide 44 and the spring 46. Therefore, the threadedconnection 124 between the spring adjustment screw 70 and the rearspring guide 44 cause the rear spring guide 44 to travel forward whenthe pressure adjustment knob 66 is turned clockwise. Likewise, the rearspring guide 44 travels rearward when the pressure adjustment knob 66 isturned counterclockwise. The movement of the front spring guide 42,however, is restricted by the stops 48 which limit the travel range ofthe front spring guide 44 between a forward-most position and arearward-most position. As a result, the user is able to adjust thecompression in the main spring 46 so that a correspondingly greater orlesser amount of resistance is felt by the user when reclining the back14.

[0089] The spring adjustment screw 70 is prevented from travelingforward or rearward during rotation by a rear shoulder 72 on the spiralbevel gear 68 and a front shoulder 73 on the screw 70. The rear shoulder72 abuts against the back face of a fixed support wall 126 formed intothe base 36. The front shoulder 73 is located on the opposite side ofthe support wall 126 and abuts against a thrust washer 76. The thrustwasher 76 then abuts against a lip 75 on the bushing 74, which abutsagainst the front face of the support wall 126. The bushing 74 ismounted onto the shaft portion 129 of the spring adjustment screw 70 andis installed within an inner diameter 128 formed into the support wall126. The bushing 74 includes a Teflon impregnated mesh along itsinterior to allow the shaft portion 129 to smoothly rotate against thebushing's 74 inner diameter. The lip 75 of the bushing 74 also includesa Teflon impregnated mesh on the surface that contacts the thrust washer76 to also ensure smooth rotation of the screw 70.

[0090] A cover 130 is also provided that is installed over the spiralbevel set 68 and the bushing 74 and is secured in place by screws 132that are threaded into the base 36. The cover 130 traps the springadjustment screw 70 along the top 129 of the screw 70 to restrain thescrew 70 within the inner diameter 128 formed in the support wall 126. Aportion of the inner diameter 128 is also formed into the bottom side ofthe cover 130 to support the top of the bushing 74.

[0091] A preload member 134 is also formed into the cover 130. Thepreload member 134 is attached along each end 136 to the cover 130 andhas a relatively small cross-section so that the preload member 134 ismoderately flexible. In the preferred embodiment, the preload member 134and the cover 130 are made from a material known by those skilled in theart as acetyl, or sometimes referred to as Delrin. Preferably, thespring rate of the preload member 134 is about 40 lb/in. The preloadmember 134 includes a central portion 138 with a partial inner diameter139 and two outer portions 140. The two outer portions 140 are curveddownwards and connect the central portion 138 to the two ends 136 thatare attached to the cover 130.

[0092] The rear spring guide 44 is adapted for the preload member 134 byincluding a rear shoulder 142. The outer diameter 144 of the rearshoulder 142 is about equal to the outer diameter of the thrust washer76. Unlike the inner threaded section 124 of the spring guide 44, theinterior of the rear shoulder 142 is unthreaded and has an innerdiameter 146 larger than the threads of the screw 70 and slightly largerthan the front shoulder 73 of the screw 70. Thus, when the rear springguide 44 is threaded rearward to its rearward-most position, the innerdiameter 146 of the shoulder 142 will be positioned over the outerdiameter 150 of the front shoulder 73 of the screw 70. The back face 148of the shoulder 142 will then abut against the thrust washer 76 and theouter diameter 144 of the shoulder 142 will be about flush with theouter diameter of the thrust washer 76.

[0093] The partial inner diameter 139 of the preload member 134 isshaped and positioned to rest upon the outer diameter 150 of the frontshoulder 73 of the screw 70 in its free state. However, the preloadmember 134 is sufficiently flexible to rest upon the larger outerdiameter 144 of the rear shoulder 142 of the rear spring guide 44 also.

[0094] Accordingly, the preload member 134 allows the spring assembly122 to be installed without having to compress the main spring 46 eithermanually or with special tools. Initial compression can then beintroduced to the main spring 46 by simply turning the pressureadjustment knob 66. To install the spring assembly 122, the rear springguide 44 is first threaded rearward into its rearward-most position, ora first position, so that the back face 148 of the rear shoulder 142abuts against the thrust washer 76. The preload member 134 is theninstalled so that it rests on top of the rear shoulder 142 of the springguide 44 in a slightly tensioned state. The main spring 46 and the otherpieces of the assembly 122 can then be installed without any compressionof the main spring 46 necessary. When the entire spring assembly 122 isinstalled in this initial state, a small amount of looseness will existbetween the individual pieces of the spring assembly 122. To remove thislooseness, the pressure adjustment knob 66 is turned clockwise to forcethe rear spring guide 44 forward. Because no initial compression willexist in the main spring 46, the rear spring guide 44 may need to beheld with one hand to prevent rotation of the spring guide 44. When therear spring guide 44 travels forward at least the distance of the widthof the preload member 134, the preload member 134 will pop down into itsfree state and will rest on top of the outer diameter 150 of the frontshoulder 73 of the screw 70.

[0095] In the preferred embodiment, the width of the preload member 134is about 0.090 inch. Therefore, after the preload member 134 pops downonto the front shoulder 73 of the screw 70, an initial compression, orstress, in the main spring 46 will be indefinitely preserved.Accordingly, after the initial installation procedure, the rear springguide 44 will be prevented from returning to its rearward-most positionthat existed before the installation procedure. Thus, after theinstallation procedure, if the user turns the pressure adjustment knob66 so that the rear spring guide 44 travels rearward, the back face ofthe shoulder 142 of the spring guide 44 will now abut against thepreload member 134 instead of the thrust washer 76. Because the preloadmember 134 is then compressed between the thrust washer 76 and the backface of the spring guide shoulder 142, the user is prevented fromremoving the initial compression that has been introduced into the mainspring 46.

Removable Arm Rests and Plugs System

[0096] In order to satisfy the wide range of user preferences for chairoptions, a modular system has been provided for the arm rests 210, 310of the chair 10, 300. This modular system includes arm rests 210, 310and plugs 270, 380 for both a task chair 10 with a reclining system anda four legged chair 300 commonly used for stacking. In order to reducemanufacturing costs, the modular system provides a single back 14 thatcan be used on both the task chair 10 and the stacker chair 300. A setof removable arm rests 210, 310 are also provided, with one arm rest 210being adapted for the task chair 10 and another arm rest 310 beingadapted for the stacker chair 300. A similar set of plugs 270, 380 arealso provided, one 270 for the task chair 10 and another 380 for thestacker chair 200. Accordingly, the arm rests 210, 310 can be removedand the chair 10, 300 can be used without arm rests 210, 310 by usingthe plugs 270, 380 instead. The two arm rests 210, 310 and the two plugs270, 380 are all adapted to be used with the single back 14. Thus, themodular system provides an increased number of possible chairconfigurations. In addition, the user can reconfigure the chair from theinitial configuration if desired. Of course, it should be understoodthat either set of arm rests 210, 310 or plugs 270, 380 could be adaptedfor either chair 10, 300.

[0097] Referring now to FIGS. 1, 15, 16, 17, 18, 20, and 21, the taskchair arm rest 210 includes an arm rest portion 212 along the top sideof the arm rest 210 that is shaped so that the user can comfortably resthis arm upon the top of the arm rest portion 212. The arm rest portion212 is made from a moderately soft material to increase comfort, such asrubber or foam. The arm rest 210 also includes a connecting member 214along the bottom side of the arm rest 210 that is used to connect thearm rest 210 to the frame 30 of the chair 10. Preferably, the connectingmember 214 is made from an iron material that is cast in a sand mold.The arm rest portion 212 and the connecting member 214 are permanentlyattached to each other to form a rigid arm rest 210.

[0098] The connecting member 214 extends downward in a tapered shapewith the bottom end being narrower than the upper end. As is well-knownby those skilled in the art of said castings, a certain amount of draft,or downward slope, is required to manufacture the cast iron connectingmember 214. This necessary draft angle has been advantageouslyincorporated into the connecting system to provide a secure and tightfit between the arm rest 210 and the chair 10. Accordingly, theconnecting member 214 includes a front 216 and rear 217 rounded surfacethat tapers downward about 2.5° on each surface. The connecting member214 also includes an inside 218 and outside 219 flat surface that tapersdownward about 1.5° on each surface. Similarly, the yoke 32 of the chair10 includes an interior cavity 220 with corresponding rounded surfaces222 and flat surfaces 224 that are also tapered.

[0099] Along the top side of the connecting member 214, an inner andouter anti-rotation tab 226 is provided. The anti-rotation tabs 226extend below the frame stop surfaces 228, and the exterior surface ofthe tabs 226 form a rounded guide diameter 230. The outer guide diameter230 extends upward to the top end of the connecting member 214. Theframe stop surfaces 228 are positioned along each side of theanti-rotation tabs 226 and extend diametrically from the tapered flatsurface 218, 219 to the outer guide diameter 230. The top side of theconnecting member 214 also includes back stop surfaces 232 that arepositioned above the frame stop surfaces 228. The back stop surfaces 232extend diametrically from the inner guide diameter 228 to the outerguide diameter 230. Finally, a tapered receiving hole 234, or receiver,is included along the bottom side of the connecting member 214 thatextends through the inside flat surface 218.

[0100] The yoke 32, or frame 32, includes anti-rotation slots 236 thatcorrespond to the anti-rotation tabs 226. In addition, the yoke 32includes a mounting surface 238 along the top of the yoke 32 thatcorresponds to the frame stop surfaces 232. Lastly, a threaded hole 240is included, which corresponds to the receiving hole 234, that extendsthrough the inside wall of the yoke 32 to the bottom of the interiortapered cavity 220.

[0101] Preferably, the back 14 is made from 20% glass filledpolypropylene. To increase the comfort of the back 14, the back 14 isperforated with a number of holes to increase aeration. The back 14includes a left arm rest hole 242 and a right arm rest hole 243 thatextend through the back 14. The arm rest holes 242 include an upperguide diameter 244 that corresponds to the arm rest outer guide diameter230. A lower guide diameter 246 is also included that corresponds to theouter diameter 239 of the yoke 32. Near the top side of the arm resthole 242 is a front 248 and a rear 249 ledge. The ledges 248, 249 havetop surfaces 250 that correspond to the back stop surfaces 232 andextend diametrically from an inner diameter 252 slightly larger than theinner guide diameter 229 of the connecting member 214, 228 to the upperguide diameter 244. The ledges 248, 249 extend only around the front andthe rear of the arm rest hole 242 and do not extend around the sides ofthe arm rest hole 242.

[0102] Four wedges 254 are also included along the inner diameter 252 ofthe ledges 248, 249. The wedges 254 extend downward from the top of theledges 248, 249 to the bottom of the ledges 248, 249. The wedges 254 arepositioned near each edge of the ledges 248, 249. The wedges 254 areshaped with a downward sloping ramp that extends further in towards thecenter of the arm rest hole 242 near the bottom of the ledge 248, 249than near the top of the ledge 248, 249.

[0103] From the foregoing description, it is apparent that the arm rest210 can be easily connected to the yoke 32 to provide a secure and tightfit between the arm rest 210, the yoke 32, and the back 14. Accordingly,in order to install the arm rest 210, the back 14 is first installedover the yoke 32. The lower guide diameter 246 of the back 14 fitssnugly around the outer diameter 239 of the yoke 32. The bottom surfaces251 of the ledges 248, 249 in the arm rest hole 242 will then abutagainst the top mounting surface 238 of the yoke 32.

[0104] Next, the arm rest 210 is installed through the arm rest hole 242in the back 14 and into the interior cavity 220 of the yoke 32. Theframe stop surfaces 228 will then be located near the top mountingsurface 238 of the yoke 32, and the back stop surfaces 232 will belocated near the top surface 250 of the ledges 248, 249 in the arm resthole 242. The anti-rotation tabs 226 of the arm rest 210 also slide downinto the anti-rotation slots 236 in the yoke 32.

[0105] Finally, a set screw 252 is threaded into the threaded hole 240of the yoke 32, with the nose 254 of the set screw 252 extending intothe receiving hole 234 of the connecting member 214. When the set screw252 is tightened the connection between the arm rest 210, the yoke 32,and the back 14 becomes rigid and secure. It is believed that severaldifferent features contribute to the rigidity of the connection. First,the threaded hole 240 in the yoke 32 is offset below and towards theinside from where the receiving hole 234 is expected to be positioned.Because the receiving hole 234 is tapered about 100 per side, and theset screw nose 254 is tapered about 150 per side, a wedge is formedbetween the set screw nose 254 and the receiving hole 234 which pullsthe connecting member 214 towards the threaded hole 240. Preferably, thethreaded hole 240 is offset about 0.035 inch down from the expectedposition of the receiving hole 234. Therefore, tightening of the setscrew 252 will force the connecting member 214 downward and deeper intothe interior cavity 220 of the yoke 32. Because the surfaces 222, 224 ofthe interior cavity 220 are tapered like the connecting member surfaces216, 217, 218, 219, the connecting member 214 will wedge tightly intothe interior cavity 220. Alternatively, the connecting member 214 couldbe forced downward until either the frame stop surfaces 228 abut againstthe top mounting surface 238 of the yoke 32 or the back stop surfaces232 abut against the top surfaces 250 of the arm rest hole ledges 248,249. Preferably, the threaded hole 240 is also offset about 0.030 inchinside from the expected position of the receiving hole 234. Therefore,the connecting member 214 will be rotated inward by the set screw 252until the anti-rotation tabs 226 abut against the anti-rotation slots236 in the yoke 32. Offsetting the threaded hole 240 towards the insideis believed to be desirable over positioning the threaded hole 240towards the outside because side impacts to the arm rest 210 will betransferred to the yoke 32 through the anti-rotation tabs 226 instead ofbeing absorbed by the set screw 252. It should be understood that otheroffset positions between the threaded hole 240 and the receiving hole234 would also provide a tight connection. The set screw 252 furthertightens the connection between the connecting member 214 and the yoke32 by pushing the bottom of the connecting member 214 outwards and awayfrom the threaded hole 240. As the nose 254 of the set screw 252contacts the tapered sides of the receiving hole 234, leverage iscreated between the receiving hole 234 at the bottom of the connectingmember 214 and the top of the connecting member 214. This wedges theconnecting member 214 even tighter into the interior cavity 220 of theyoke 32.

[0106] The wedges 254 on the inner diameter 252 of the ledges 248, 249in the back 14 also contribute to the rigidity of the connection. Thebottom ends of the ramped wedges 254 form an inner diameter that issmaller than the inner diameter 229 of the connecting member 214.Therefore, when the arm rest 210 is installed through the arm rest hole242, an interference fit will occur between the inner guide diameter 229of the connecting member 214 and the wedges 254. However, the wedges 254are relatively narrow in width and are made from a material that iscompressible. Thus, when the inner guide diameter 229 of the connectingmember 214 is forced through the wedges 254, the wedges 254 willcompress slightly to allow the inner guide diameter 229 to pass throughthe wedges 254. The resulting connection between the wedges 254 and theinner guide diameter 229 is a tight, compressive fit.

[0107] Turning now also to FIGS. 22 through 24, a plug 270 is providedin order to satisfy users of the task chair 10 who prefer not to use armrests 210. The plug 270 is molded from a nylon material.

[0108] Along the top side of the plug 270, a cap 272 is provided thathas a smoothly rounded, textured surface for an attractive appearance.The bottom side of the cap 272 forms a back stop surface 274. The backstop surface 274 extends diametrically from the outer diameter 273 ofthe cap 272 to the inner guide diameter 276. Frame stop surfaces arealso provided along each side of the anti-rotation tabs 280. The framestop surfaces 278 extend diametrically from the tapered flat surfaces288, 289 to the outer guide diameter 282. The anti-rotation tabs 280 areprovided along the inner and outer sides near the top of the plug 270.The anti-rotation tabs 280 extend below the frame stop surfaces 278 andoutwards to the outer guide diameter 282. Along the front side of theplug 270, an installation tab 284 is provided that extends downward fromthe back stop surface 274 and outwards from the inner guide diameter276.

[0109] Along the bottom side of the plug 270, a front 286 and rear 287rounded surface and an inside 288 and an outside 289 flat surface areprovided. The rounded surfaces 286, 287 and the flat surfaces 288, 289are tapered so that they slope inward from the top side of the plug 270to the bottom side of the plug 270. The inside flat surface 288 isdisconnected along the sides from the front and rear rounded surfaces286, 287. This disconnected portion forms a spring member 290 that isangled slightly outward from the inward sloping upper portion 291 of theinside flat surface 288. Preferably, the spring member 290 has a springrate of about 40 lb/in. At the bottom end of the spring member 290, arounded detent nose 292 is provided that extends outward in thedirection of the outward angle of the spring member 290.

[0110] From the foregoing description, it is apparent that the plug 270can be installed into the yoke 32 and the back 14 to provide a secureconnection between the yoke 32 and the back 14 without the need for anarm rest 210. Accordingly, to install the plug 270, the back 14 is firstinstalled over the yoke 32 by sliding the lower guide diameter 246 ofthe arm rest hole 242 over the outer diameter 239 of the yoke 32 untilthe bottom surfaces 251 of the ledges 248, 249 abut against the topmounting surface 238 of the yoke 32. The plug 270 is then installedthrough the arm rest hole 243 in the back 14 and into the interiorcavity 220 of the yoke 32. The plug 270 is pressed down until the detentnose 292 of the spring member 290 is aligned with the threaded hole 240,or receiver, in the yoke 32. Because the outward angle of the springmember 290 causes an interference fit between the spring member 290 andthe interior cavity 220 of the yoke 32, the detent nose 292 will popoutward and into the threaded hole 240 when the detent nose 292 and thethreaded hole 240 become aligned.

[0111] When the detent nose 292 pops into the threaded hole 240, theframe stop surfaces 278 will abut or be near the top mounting surface238 of the yoke 32. The back stop surface 274 will also abut or be nearthe top side 250 of the ledges 248, 249 in the back 14. At the sametime, the tapered rounded surfaces 286, 287 and the tapered flatsurfaces 288, 289 will be wedged into the tapered interior cavity 220 ofthe yoke 32. The detent nose 292 will then prevent the back 14 frombeing disconnected from the yoke 32 by restraining the ledges 248, 249in the back 14 under the back stop surface 274 of the plug 270.

[0112] The anti-rotation tabs 280 of the plug 270 also slide down intothe anti-rotation slots 236 of the yoke 32. The anti-rotation tabs 280,thus, prevent the plug 270 from rotating and possibly dislodging thedetent nose 292 from the threaded hole 240.

[0113] The connection between the plug 270 and the yoke 32 is furthertightened by the wedges 254 on the inner diameter 252 of the ledges 248,249 in the back 14. Like the arm rest inner guide diameter 229, theinner guide diameter 276 of the plug 270 compresses the wedges 254 toprovide a tight, compressive fit.

[0114] Finally, the installation tab 284 slides into the installationslot 294 in the back 14. The installation slot 294 extends down throughthe front ledge 248 in the left arm rest hole 242 and through the rearledge 249 in the right arm rest hole 243. The installation tab 284allows a single plug 270 to be used for both the left arm rest hole 242and the right arm rest hole 243 of the chair 10. The installation tab284, thus, prevents the plug 270 from being installed with the detentnose 292 facing in the opposite direction of the threaded hole 240,where it would not adequately connect the back 14 to the yoke 32. Thisfeature is useful for assembly line manufacturing, where the monotony ofrepeated assembly tasks can lead to inattention and improperinstallation of the plugs 270. The installation tab 284 is alsoespecially useful for chairs 10 that are sold unassembled directly tousers. Because users are not familiar with the proper functioning of theplugs 270, it is likely that some users will improperly install theplugs 270, and thus, cause later dissatisfaction with the chair 10 whenthe back 14 does not remain securely fastened to the yoke 32.

[0115] Turning now to FIGS. 15, 16, and 25 through 31, an arm rest 310for a stacker chair 300 is provided. The arm rest 310 includes an armrest portion 312 along the top side that is made from a soft,comfortable material. Along the bottom side of the arm rest 310, aconnecting member 314 is provided. The connecting member 314 is madefrom aluminum that is cast in a permanent mold. The arm rest portion 312and the connecting member 314 are permanently attached to each other toform a rigid arm rest 310.

[0116] Along the top side of the connecting member 314, back stopsurfaces 316 are provided that extend diametrically from the outer guidediameter 318 to the inner guide diameter 320. Frame stop surfaces arealso provided below the back stop surfaces 322. The frame stop surfaces322 are positioned along each side of the anti-rotation tabs 324 andextend diametrically from the inner guide diameter 320 to the outerguide diameter 318. The anti-rotation tabs 324 are positioned along theinside and the outside of the connecting member 314 and extend downwardfrom the frame stop surfaces 322.

[0117] Guide pads 326, 327 are provided above the anti-rotation tabs324. The guide pads 326, 327 extend between the inner guide diameter 320and the outer guide diameter 318 and between the frame stop surfaces 322and the back stop surfaces 316. When directly viewing either of guidepads 326, 327 of the left arm rest 310 from the front side of the pad326, 327, the guide pads 326, 327 include a flat side 328 on the leftside of the guide pad 326, 327 and an angled side 330 on the right sideof the guide pad 326, 327. The angle of the angled side 330 is about100, with the lower end of the angled side 330 sloped inward from theupper end. When viewed with the left arm rest 310 installed in the chair300, the angled side 330 of the inside guide pad 326 will face forward,and the angled side 330 of the outside guide pad 327 will face rearward.

[0118] Along the bottom side of the connecting member 314, the innerguide diameter 320 extends downward from the top side of the connectingmember 314 down to the bottom of side of the connecting member 314. Nearthe bottom of the connecting member 314, a retention hole 332 isprovided for a detent assembly 352, 356. Just below the retention hole332, an angled O-ring groove 334 is provided. The O-ring groove 334 isangled with the rear side of the O-ring groove 334 being lower than thefront side of the O-ring groove 334.

[0119] The frame 340 of the stacker chair 300 is provided with aninterior cavity 342 that is straight and non-tapered. An outer diameter344 is also provided. Along the top side of the frame 340, a mountingsurface 346 is included. Anti-rotation slots 348 extend downward fromthe mounting surface 346 and through the frame wall. The anti-rotationslots 348 are positioned on the inside and on the outside of the frame340. Below the mounting surface 346, a detent hole 350, or receiver, isprovided that extends through the inside wall of the frame 340.

[0120] Two different detent assemblies 352, 356 are provided. Bothdetent assemblies 352, 356 have a cylindrical housing 362 with a spring(not shown) installed within the housing 362. A detent nose 354, 358extends out from one end of the housing 362. The detent nose 354, 358can be pressed inward against the spring 364 but will extend outward inits free state. One detent assembly 352 has a detent nose 354 with auniformly rounded end. Another detent assembly 356 has a detent nose 358with angled sides. The angled sides are angled about 180 on each side.Below the angled sides is a straight portion 362 that has a uniformouter diameter.

[0121] From the foregoing description, it is apparent that the arm rest310 can be easily connected to the frame 340 to provide a secure andtight fit between the arm rest 310, the frame 340, and the back 14.Accordingly, in order to install the arm rest 310, the back 14 is firstinstalled over the frame 340 of the stacker chair 300. The lower guidediameter 246 fits snugly around the outer diameter 344 of the frame 340.The bottom surface 251 of the ledges 248, 249 will then abut against thetop mounting surface 346 of the frame 340.

[0122] Next, the arm rest 310 is installed through the arm rest hole 242in the back 14 and into the interior cavity 342 of the frame 340. Toprepare the arm rest 310 for installation, an O-ring (not shown) isfirst installed into the O-ring groove 334 along the bottom side of theconnecting member 314. One of the detent assemblies 352, 356 is alsoinstalled into the retention hole 332, with the detent nose 354, 358facing towards the inside of the connecting member 314. The detentassembly 352 with the rounded detent nose 354 is preferred when the armrest 310 is installed in a manufacturing assembly line. However, whenthe arm rest 310 is shipped unassembled and will be installed by a user,the detent assembly 356 with the angled detent nose 358 is preferred.

[0123] The connecting member 314 is then inserted into the arm rest hole242 with the arm rest portion 312 facing outwards. This will allow therear side of the O-ring, which is angled downward, to enter the arm resthole 242 before the front side of the O-ring. Accordingly, the rear sideof the O-ring will travel down the arm rest hole 242 ahead of the frontside and will slide down between the front and rear ledges 248, 249 toallow easier installation of the arm rest 310.

[0124] A detent ramp 368 has been provided next to the installation slot294 in the front ledge 248 in order to further ease installation of thedetent assembly 352, 356. The detent ramp 368 extends downward andinward from the upper guide diameter 244 of the left arm rest hole 242near the top side of the front ledge 248. The detent ramp 368 is lessnecessary when the rounded nosed detent assembly 352 is used but isespecially helpful when the angled nosed detent assembly 356 is used.Thus, as the connecting member 314 is pressed down through the arm resthole 242, the detent ramp 368 will gradually force the nose 354, 358 ofthe detent assembly 352, 356 inward to ease the detent nose 354, 358past the top surface 250 of the ledge 248. Because the detent nose 354,358 will be facing rearward when the arm rest 310 is installed in theright arm rest hole 243, the detent ramp 368 extends through the rearledge 249 of the right arm rest hole 243.

[0125] Once the detent assembly 352, 356 passes by the front ledge 248,the arm rest 310 can be rotated forward so that the arm rest portion 312faces forward, the connecting member 314 is then pressed down until theanti-rotation tabs 324 slide into the anti-rotation slots 348 and thedetent nose 354, 358 pops through the detent hole 350 in the frame 340.

[0126] In order to provide a rigid connection between the arm rest 310,and the back 14, and the frame 340, an angled side 370 has been providedon the inside edge of the front ledge 248 and on the outside edge of therear ledge 249. The angled sides 370 of the ledges 248, 249 correspondto the angled sides 330 of the guide pads 326, 327 on the connectingmember 314. The position of the angled sides 330, 370 can be reversed,but the present configuration is preferred because side impacts to thearm rest 310 will be transferred away from the angled side 330 and willbe absorbed by the straight sides instead. When installed, the guidepads 326, 327 will become wedged between the front and rear ledges 248,249, with the angled sides 330 of the guide pads 326, 327 abuttingagainst the angled sides 370 of the ledges 248, 249. In a manufacturingassembly line, about 100 lbs. of downward force can be applied to thearm rest 310 to wedge the guide pads 326, 327 against the ledges 248,249 until the rounded detent nose 354 pops into the detent hole 350. Theledges 248, 249 are made from a compressible material that will deformslightly when pressure is applied from the angled sides 330 of the guidepads 326, 327. In contrast to a manufacturing assembly line, when a userinstalls the arm rest 310, the angled nosed detent assembly 356 ispreferred because it allows less force to be applied while stillproviding a satisfactory wedge between the guide pads 326, 327 and theledges 248, 249. Thus, when a smaller amount of downward force isapplied to the arm rest 310, the angled nose 358 of the detent assemblywill still partially pop into the detent hole 250. The angled nose 358will then securely lock the detent assembly 356 to the detent hole 350by wedging against the sides of the detent hole 350. Over time, duringnormal use of the chair 300, the angled detent nose 358 will furtherstrengthen the connection as the connecting member 314 is slowly presseddeeper into the frame 341 by ramping further into the detent hole 350.Eventually, the angled detent nose 358 may pop all the way through thedetent hole 350, and the straight portion 360 will provide a solid lockagainst the sides of the detent hole 351.

[0127] The connection is further tightened at the top by the wedges 254on the inside diameter 252 of the ledges 248, 249. The wedges 254contact the inner guide diameter 320 of the connecting member 314 andcreate an interference fit between the inner guide diameter 320 and thewedges 254. As the connecting member 314 is pressed downward, the wedges254 will compress slightly to allow the connecting member 314 to passthrough the ledges 248, 249. As a result, a tight compressive fit willoccur between the wedges 254 and the top part of the inner guidediameter 320. Along the bottom of the connection member 314, theconnection will be tightened by the O-ring 366. The O-ring 366 becomescompressed by the interior cavity 342 of the frame 340, thus, providinga further rigid connection.

[0128] Along the bottom side of the back 14, a cavity 372 has beenprovided in the back 14 to allow easy removal of the arm rest 310. Thedetent assembly 352, 356 and the detent hole 350 have been positionedabove the bottom end of the back 14. The detent nose 354, 358,therefore, protrudes out from the detent hole 350 above the bottom endof the back 14 in an area that is hidden from casual observation inorder to improve the appearance of the chair 300. The detent nose 354,358 is also protected in this arrangement from being accidentallydislodged during normal use by inadvertent contact with the detent nose354, 358. Accordingly, a detent slot 374 is provided in the back 14 forclearance of the detent nose 354, 358 that extends between the arm resthole 242 and the bottom cavity 370. Thus, the arm rest 10 can be easilyremoved by reaching into the bottom cavity 372, pressing the detent nose354, 358 back through the detent slot 374 and the detent hole 350, andlifting the arm rest 310 back out of the arm rest hole 242.

[0129] Turning now also to FIGS. 32 through 34, a plug 380 is providedin order to satisfy users of the stacker chair 300 who prefer not to usearm rests 310. The plug 380 is molded from a nylon material.

[0130] Along the top side of the plug 380, a cap 382 is provided thathas a smoothly rounded, textured surface for an attractive appearance.The bottom side of the cap 382 forms a back stop surface 384. The backstop surface 384 extends diametrically from the outer diameter of thecap 382 to the inner guide diameter 386. Frame stop surfaces 388 arealso provided along each side of the anti-rotation tabs 390. The framestop surfaces 388 extend diametrically from the inner guide diameter 386to the outer guide diameter 392. The anti-rotation tabs 390 are providedalong the inner and outer sides near the top of the plug 380. Theanti-rotation tabs 390 extend below the frame stop surfaces 388 andoutwards to the outer guide diameter 392. Along the front side of theplug 380, an installation tab 394 is provided that extends downward fromthe back stop surfaces 384 and outwards from the inner guide diameter386.

[0131] Along the bottom side of the plug 380, the inner guide diameter386 extends down to the bottom end of the plug 380. Because the moldingprocess is unable to accurately control the size of the inner guidediameter 386 along the bottom of the plug 380, guide pads 396 that canbe more easily controlled have been added. Thus, four guide pads 396 arepositioned around the inner guide diameter 386 near the bottom of theplug 380 that extend outward from the inner guide diameter 386.

[0132] A spring member 398 is also provided. The spring member 398 iscantilevered from the plug 380 and is connected to the plug 380 near thetop side of the plug 380. Preferably, the spring rate of the springmember 398 is about 20 lb/in. The spring member 398 extends downwardtoward the bottom of the plug 380 and is disconnected from the plug 380along its sides and its bottom end. The spring member 398 is also angledoutwards from the plug 380, with the bottom of the spring member 398protruding further away from the inner guide diameter 386 than theconnected top end. A detent nose 400 is provided along the bottom end ofthe spring member 398 that extends outward from the spring member 398.Finally, an upward facing catch surface 402 is formed onto the outer endof the detent nose 400.

[0133] From the foregoing description, it is apparent that the plug 380can be installed into the frame 340 and the back 14 to provide a secureconnection between the frame 340 and the back 14 without the need for anarm rest 310. Accordingly, to install the plug 380, the back 14 is firstinstalled over the frame 340 by sliding the lower guide diameter 246 ofthe arm rest hole 242 over the outer diameter 344 of the frame 340 untilthe bottom surfaces 251 of the ledges 248, 249 abut against the topmounting surface 346 of the frame 340. The plug 380 is then installedthrough the arm rest hole 242 in the back 14 and into the interiorcavity 342 of the frame 340. The plug 380 is pressed down until thedetent nose 400 of the spring member 398 is aligned with the detent hole350 in the frame 340. Because the outward angle of the spring member 398causes an interference fit between the spring member 398 and theinterior cavity 342 of the frame 340, the detent nose 400 will popoutwards and into the detent hole 350 when the detent nose 400 and thedetent hole 350 become aligned.

[0134] When the detent nose 400 pops into the detent hole 350, the framestop surfaces 388 will abut or be near the top mounting surface 346 ofthe frame 340. The back stop surface 384 will also abut or be near thetop side 250 of the ledges 248, 249. The detent nose 400 will thenprevent the back 14 from being disconnected from the frame 340 byrestraining the ledges 248, 249 in the back 14 under the back stopsurface 384 of the plug 380. Experience has shown that the back 14 ofthe stacker chair 300 is subjected to considerably more upward forcesthan the back 14 of the task chair 10. This commonly occurs when onechair 300 is stacked on top of another chair 300, thus causing an impacton the upper chair 300. Therefore, the plug 380 of the stacker chair 300experiences higher and more frequent upward forces on the cap 382. Thiscondition has been known to force the detent nose 400 out of the detenthole 350, thus allowing the back 14 to become disconnected from theframe 340. To prevent this problem, the catch surface 402 grasps theouter diameter 344 of the frame 340, which prevents the detent nose 400from being pulled back through the detent hole 350 by an upward force onthe plug 380.

[0135] As the plug 380 is installed into the back 14 and the frame 340the anti-rotation tabs 390 of the plug 380 slide down into theanti-rotation slots 348 of the frame 340. The anti-rotation tabs 390,thus, prevent the plug 380 from rotating and possibly dislodging thedetent nose 400 from the detent hole 350.

[0136] The connection between the plug 380 and the frame 340 is furthertightened by the wedges 254 on the inner diameter 252 of the ledges 248,249 in the back 14. Like the arm rest inner guide diameter 320, theinner guide diameter 386 of the plug 380 compresses the wedges 254 toprovide a tight, compressive fit. The guide pads 396 on the lower end ofthe plug 380 also contribute to a tight fit. The guide pads 396 contactthe sides of the interior cavity 342 of the frame 340, thus eliminatingany looseness between the bottom of the plug 380 and the frame 340.

[0137] Finally, the installation tab 394 slides into the installationslot 294 in the back 14. The installation tab 394 allows a single plug380 to be used for both the left arm rest hole 242 and the right armrest hole 243 of the chair 300. The installation tab 394, thus, preventsthe plug 380 from being installed with the detent nose 400 facing in theopposite direction of the detent hole 350, where it would not adequatelyconnect the back 14 to the frame 340. Correct installation of the plug380 is particularly important in the stacker chair 300 because of theincreased upward forces on the back 14 that are likely to dislodge theplug 380 as previously described. The installation tab 394 is useful forassembly line manufacturing, where the monotony of repeated assemblytasks often lead to inattention and improper installation of the plugs380. The installation tab is also especially useful for chairs 300 thatare sold unassembled directly to users. Because users are not familiarwith the proper functioning of the plugs 380, it is likely that someusers will improperly install the plugs 380, and thus, cause laterdissatisfaction with the chair 300 when the back 14 does not remainsecurely fastened to the frame 340.

[0138] Like the arm rest 310 for the stacker chair 300, the detent noseof the plug 380 is hidden above the bottom 460 side of the back 14within the detent slot 374 in the back 14 to improve the appearance ofthe chair 300 and protect the detent nose 400 from accidentaldislodging. Accordingly, the plug 380 can be easily removed by reachinginto the bottom cavity 372, pressing the detent nose 400 back throughthe detent slot 374 and the detent hole 350, and lifting the plug 380back out of the arm rest hole 242.

Fabric Seat

[0139] Referring now to FIGS. 35 through 41, 43 through 47, and 49through 53, a method of manufacturing the fabric seat 12 is provided. Avariety of fabric materials 450 may be used with the fabric seat 12. Thepreferred fabric material 450, however, is a knit material 450. Oneexample of a knit material 450 that may be used is the fabricmanufactured by Milliken under the product name Flexnet. This knitfabric material 450 differs from woven fabric materials because thethreads of the fabric 450 are interlocked together to prevent singlethreads from being pulled loose, as is possible with woven fabrics. Thepreferred fabric 450 also includes holes through the fabric 450 that areformed between the lateral and the longitudinal threads of the fabric450. In addition, the lateral threads preferably include elastomerthreads, while the longitudinal threads include polyester threads. Theelastomer threads are desirable because they allow the fabric 450 to bestretched further in the lateral direction than in the longitudinaldirection.

[0140] The fabric seat 12 includes a seat frame 454 and a cover 456 thatgrasps the fabric 450 around the circumference of the seat 12 in orderto maintain a tight stretch in the fabric 450. Preferably, the seatframe 454 and the cover 456 are molded from a 20% glass filledpolypropylene material, but other materials may be used also. The seatframe 454 also provides an attaching system for rigidly installing theseat 12 onto the frame 30, 340 of the chair 10, 300. To improve thecomfort of the fabric seat 12, a cushion 458 is installed under thefabric 450 along the front of the seat 12 to provide a resting area forthe user's legs.

[0141] The fabric 450 is securely attached to the seat frame 454 with aseries of teeth 460, or grasping members 460, that have been providedaround the circumference of the seat frame 454. The teeth 460 extend upfrom the seat frame 454 and are smoothly contoured so that the top ofeach tooth is rounded and smaller and the base of the tooth 460 isbroader. In addition, each tooth 460 includes an undercut area 462 alongthe outside of the tooth 460. A raised ridge 464 is also provided alongthe inside of the teeth 460 that extends up to about the height of theteeth 460. A recessed channel 466 is formed between the teeth 460 andthe raised ridge 464 which extends up from the base of the teeth 460 tothe top of the raised ridge 464. Accordingly, the teeth 460 securelyretain the fabric 450 by protruding up through the holes in the fabric450 that are formed between the lateral and longitudinal threads. Inaddition, the undercut areas 464 prevent the fabric 450 from dislodgingfrom the teeth 460 by securely grasping the fabric holes. The raisedridge 464 provides support for the fabric 450 when a user sits on theseat 12.

[0142] Once the fabric 450 has been installed onto the teeth 460 of theseat frame 454, the cover 456 is installed on top of the outercircumference of the seat frame 454. Preferably, the cover 456 isflexible and includes snaps so that it can be easily installed onto theframe 454. Clips 468 can also be provided along the bottom side of theseat 12 to further secure the seat frame 454 and the cover 456 together.Accordingly, the clips 468 snap into a receiver 455 on the seat frame454 and a receiver 457 on the cover 456. Therefore, the cover 456 trapsthe fabric 450 between the seat frame 454 and the cover 456 to furtherprevent dislodging of the fabric 450. The cover 456 also provides asmooth exterior surface for both aesthetic purposes and to prevent theuser from snagging his clothes on the fabric joint.

[0143] In order to simplify installation of the seat 12 onto the chairframe 30, 340, an attaching system that uses a headed pin 470 andtinnerman nut 472 is also provided. Therefore, four retention slots 474are provided along the bottom side of the seat frame 454 for the headedpin 470. The retention slots 474 include a first hole 476 that is largeenough for the head 469 of the pin 470 to pass through. A second hole478 is also included that is connected to the first hole 476. The secondhole 478 is smaller than the first hole and is about the diameter of theshaft 471 of the pin 470. Retention pads 480 separate the first 476 andsecond 478 holes. A retention tab 482 is also provided above the secondhole 478.

[0144] Accordingly, the seat 12 is attached to the chair frame 30, 340by first installing the headed pins 470 into the retention slots 474.Each pin 470 is installed by inserting the head 469 up through the firsthole 476 of the retention slot, 424. The pin 470 is then pressed outwardand into the second hole 478. The retention pads 480 provide a smallamount of interference with the shaft 471 of the pin 470 so that the pin470 must be snapped into the second hole 478. The retention pads 480will then prevent the pin 470 from dislodging from the second hole 478.The seat 12 can then be installed onto the chair frame 30, 340 byinserting the shafts 471 of the pins 470 down through holes 484 in thechair frame 30, 340. The retention tabs 481 assist installation byobstructing upward movement of the head 469 of the pin 470. After theseat 12 has been installed onto the chair frame 30, 340, a tinnerman nut472 can be pressed onto the bottom end of the pin 470 to prevent theseat 12 from being detached from the chair frame 30, 340. Because asignificant amount of the force is usually required to press thetinnerman nut 472 onto the shaft 471 of the pin 470, it is preferable touse an assembly tool that contacts the top of the head 469 of the pin470 to resist the pressing force. Alternatively, the retention tab 482can also be used to resist the pressing force, thereby eliminating theneed for the assembly tool.

[0145] Turning now to FIGS. 47 and 49 through 53, a method of attachingthe fabric 450 to the seat frame 454 is provided. As shown in FIGS. 47and 48, a machine 490 is included for easily and reliably installing thefabric 450 onto the series of teeth 460. The machine 490 uses hydraulicsfor most of the clamping and moving functions but other sources of powercould also be used. The machine 490 installs the fabric 450 onto theseat frame 454 in a two station operation 492, 494. The first station492 is a loading and pre-stretching station. The second station 494 islocated rearward from the first station 492 and includes a pressingmember 514 that forces the fabric 450 onto the teeth 460 of the seatframe 454. To move the seat frame 454 and the fabric 450 from the firststation 492 to the second station 494, a moveable base 496 is providedthat is mounted onto rails (not shown) and is moved back and forth witha cylinder (not shown). The clamps 504, 506 and the support 498 for theseat frame 545 are attached to the moveable base 496 so that the entireassembly moves between the two stations 492, 494.

[0146] The machine 490 is operated by first positioning the seat frame454 down onto the support 498. In order to fully support the entirecircumference of the seat frame 454, the support 498 is made form apoured urethane so that the shape of the support 498 matches theexterior of the bottom of the seat frame 454. Rigid locators are alsoincluded on the support 498 along the interior of the seat frame 454 tofurther position the seat frame 454 in the desired location.

[0147] Once the seat frame 454 has been accurately positioned, arectangular piece of fabric 450 is laid over the seat frame 454. Becausethe fabric 450 has visually discernible lateral threads and longitudinalthreads, accurate positioning of the fabric 450 relative to the seatframe 454 is important to satisfy appearance criteria for the seat 12.Therefore, a laser beam 500 is provided that shines a visible linelaterally across the top of the fabric 450. The operator can then usethe laser beam 500 as a guide to visually line up the lateral threads ofthe fabric 450 with the laser beam 500 to ensure that the fabric 450 isstraight.

[0148] Clamping pins 502, 503 are also attached to the bottom face ofeach of the side clamps 504. The clamping pins 502, 503 extend upwardand are received by recessed pockets in the top face of thecorresponding side clamp 504 when the clamps 504 are engaged. Three setsof clamping pins 502, 503 are included, with the first set 502 beinglocated along the front end of the side clamps 504, the second set 502being located along the rear end of the side clamps 504, and the thirdset 503 being located at the center of the side clamps 504. The centerclamping pins 503 are used in conjunction with the laser beam 500 toaccurately position the fabric 450. Accordingly, the laser beam 500shines over the two center clamping pins 503 so that the operator canline up the threads with the beam 500 and then secure the alignment bypressing the fabric 450 down onto each of the center clamping pins 502.Therefore, the pins 502, 503 are approximately equal in diameter to theholes in the fabric 450 so that the fabric 450 can be easily butsecurely pressed onto the clamping pins 502, 503. After aligning thefabric 450, the operator then presses the fabric 450 onto the front andrear sets of clamping pins 502.

[0149] The fabric 450 is next pre-stretched in an over-stretchingoperation.

[0150] The pre-stretch applies an excess stretch to the fabric 450 thatis higher than the final stretch to prevent the fabric 450 fromloosening and losing its final stretch over time. Accordingly, the frontand rear clamps 506 engage the fabric 450 and apply a small amount ofinitial tension to the fabric 450 before the side clamps 504 engage.This initial forward and rearward tension is helpful in order to evenlyspreading out the fabric 450 along the length of the side clamps 504.Next, the side clamps 804 also engage the fabric 450. The fabric 450 isthen prestretched by the clamps 504, 506. Experimental tests with thefabric 450 described above have determined that a pre-stretch of about20% for the lateral threads and 10% for the longitudinal threadsadequately prevents loosening of the fabric 450 over time. Therefore,the front and rear clamps 506 and the side clamps 504 are pulled awayfrom each other so that the fabric 450 is stretched 20% in the lateraldirection and 10% in the longitudinal direction for a short period oftime. In this pre-stretch operation the seat frame 454 is positionedslightly below the fabric 450 to avoid interference between the fabric450 and the seat frame 454.

[0151] After the pre-stretch operation is complete, the clamps 504, 506release the tension on the fabric 450. The moveable base 496, along withthe support 498 and the clamps 504, 506 is then moved rearward to thesecond station 494. Next, the final stretch is applied to the fabric450. The amount of final stretch to be used is determined primarilybased on comfort tests of the stretched seat 12. Accordingly, a higherstretched fabric 450 results in a stiffer, more rigid seat 12; and alower stretch results in a softer, more compliant seat 12. Comfort testshave determined that a final stretch of about 6% to 8% from side-to-sideand about 4% from the front-to-back is preferred. Alternatively, anon-constant final stretch can be provided, with the side-to-sidestretch being about 10% near the front of the seat 12% and 6% near theback of the seat 12. In this alternative final stretch, thefront-to-back stretch is about 4%.

[0152] Accordingly, the front and rear clamps 506 and the side clamps504 are pulled away from each other to achieve the desired finalstretch. The present machine 490 does not use actual measurements ofstretch to apply the desired stretch to the fabric 450. Instead, thestretch is achieved by applying a predetermined amount of pressure tothe tensioning cylinders. The amount of pressure to be applied isdetermined by experimental testing and is chosen to correspond to thedesired amount of fabric stretch. This system provides a relatively easymethod for controlling the fabric stretch and results in a consistentamount of final stretch in the seats 12.

[0153] To apply a non-constant lateral stretch, separate side tensioningcylinders 508, 509 are provided. Thus, a front set of tensioningcylinders 15; 508 are provided along the front side of the side clamps504, and a rear set of tensioning cylinders 509 are provided along therear side of the side clamps 504. The tensioning cylinders 508, 509 areconnected at one end to the moveable base 496 and are connected at theother end to a side clamp 504. Accordingly, the front and rear sidetensioning cylinders 508, 509 can be used to apply a non-constantlateral stretch by applying a different amount of pressure to the frontset of tensioning cylinders 508 than to the rear set of tensioningcylinders 509. To accommodate this non-constant stretch, the side clamps504 and the clamping cylinders 510 are mounted onto rotatable bases 512.Thus, the rotatable bases 512, along with the corresponding side clamps504 and clamping cylinders 510, are capable of moving outward as thestretch is applied and rotating as the lateral stretch differs fromfront to rear.

[0154] Once the final stretch has been applied to the fabric 450, thefabric 450 is installed onto the seat frame 454 by forcing the fabric450 down over the series of teeth 460 on the seat frame 454. As shown inFIG. 50, the pressing member 514, or blade 514, is first lowered so thatit is positioned slightly above the stretched fabric 450. The pressingmember 514 is approximately the width of the recessed channel 466 sothat the pressing member 514 can be pressed down into the channel 466during installation of the fabric 450. Although the recessed channel 466extends around the entire circumference of the seat frame 454, it hasbeen determined that the pressing member 514 is unnecessary for theinstallation procedure around the sides of the seat frame 454.Therefore, the pressing member 514 has been provided as a front member514 and a rear member 514 that are formed in a semi-circumference shapethat matches the recessed channel 466 along the front and the rear ofthe seat frame 454.

[0155] As shown next in FIG. 51, the support 498 is then moved upwardsso that the seat frame 454 is forced into the fabric 450. This causesthe teeth 460 and the recessed channel 466 to move upwards until thepressing member 514 enters the recessed channel 466 and abuts againstthe bottom of the channel 466. The fabric 450 is then pressed down intothe recessed channel 466 so that the fabric 450 is compressed betweenthe pressing member 514 and the seat frame 454.

[0156] As shown next in FIG. 52, a small amount of down force is appliedto the pressing member 514. A higher amount of upward force, however, isapplied to the support 498 so that the seat frame 454 and the pressingmember 514 move upward together. At the same time the seat frame 454 andpressing member 514 move up, the pressure on the tensioning cylindersare released and the tensioning cylinders move the clamps 504, 506inward towards the seat frame 454. To control the position of theoutside edge of the fabric 456, guide members 516 have been providedthat are attached to the top of each of the clamps 504, 506. The guidemembers 516 are shaped to approximately match the outer circumference ofthe seat frame 454. Thus, as the seat frame 454 moves up and the clamps504, 506 move in, the guide members 516 will pull the fabric 450 downtightly around the circumference of the seat frame 454.

[0157] As a result of pressing the fabric 450 down into the recessedchannel 466 behind the teeth 460 and pressing the fabric 450 down aroundthe outside of the teeth 460, the fabric 450 is pulled down over theteeth 460. The teeth 460 will then protrude up through the holes in thefabric 450 which are formed between the lateral and longitudinalthreads. Sometimes the teeth 460 do not fully protrude through thefabric 450, however. Therefore, a finishing procedure is provided thatis shown in FIG. 53. Accordingly, the pressing member 514 is raisedupward away from the seat frame 454. The support 498 is thenreciprocated in two cycles about 1 inch upward and downward with theguide members 516 still pulling down on the outside of the fabric 450.The speed of each cycle takes about 1 second to complete. Thesereciprocating motions further force the fabric 450 down over the teeth460 so that the teeth 460 fully protrude up through the fabric 450.

[0158] To release the seat frame 454 and the installed fabric 450 fromthe machine 12, the support 498 is lowered, the moveable base 496 ismoved back to the first station 492, and the clamps 504, 506 aredisengaged. The fabric 450 is then trimmed along the outside of theteeth 460 so that about 0.75 inch of excess fabric 450 remains aroundthe outside of the teeth 460. The cover 456 is then installed onto theseat frame 454, and the seat 12 is installed onto the chair frame 30,340 as previously described.

[0159] While a preferred embodiment of the invention has been described,it should be understood that the invention is not so limited, andmodifications may be made without departing from the invention. Thescope of the invention is defined by the appended claims, and alldevices that come within the meaning of the claims, either literally orby equivalence, are intended to be embraced therein.

We claim:
 1. A chair comprising: a first member; a second memberpivotally attached to said first member; and a third member pivotallyattached to said first member and pivotally and slidably attached tosaid second member, wherein said second member comprises an axle andsaid third member comprises a slot with an open end, said axle beingreceived in said slot through said open end.
 2. The chair according toclaim 1 further comprising a stop attached to said first member, whereinsaid stop abuts said third member and thereby restricting forward andrearward movement of said first member.
 3. The chair according to claim1 further comprising a main spring biasing said first member away from areclined position towards an upright position and an assist springbiasing said first member away from said reclined position towards anintermediate position between the reclined position and said uprightposition.
 4. The chair according to claim 1 wherein said pivotal andslidable attachment between said third member and said second membercomprises a fourth member slidably received in said slot, wherein saidaxle is pivotally attached to said fourth member and said axle extendsacross the width of said third member.
 5. The chair according to claim 1further comprising a main spring disposed between said third member andsaid axle of said second member.
 6. The chair according to claim 4further comprising a main spring disposed between a rear spring guideand a front spring guide, wherein said main spring is compressed whensaid first member moves towards a rearward position.
 7. The chairaccording to claim 6 wherein said front spring guide is attached to saidfourth member.
 8. The chair according to claim 4 further comprising astop restricting forward movement of said first member.
 9. The chairaccording to claim 8 wherein said stop is fixedly attached to said firstmember.
 10. The chair according to claim 9 wherein said stop abutsagainst a first surface of said third member and thereby restrictingforward movement of said first member.
 11. The chair according to claim10 wherein said stop restricts rearward movement of said first member byabutting a second surface of said third member.
 12. The chair accordingto claim 11 wherein said first surface and said second surface of saidthird member defines a top side and a bottom side of a stop slot in saidthird member.
 13. The chair according to claim 12 wherein said firstmember comprises a yoke, said second member comprises a seat support,said third member comprises a base, and said fourth member comprises abearing guide.
 14. The chair according to claim 13 further comprising aback attached to said yoke, a seat attached to said seat support, and achair stem assembly fixedly attached to said base in a plane transverseto said pivotal attachment between said base and said yoke.
 15. Thechair according to claim 4 further comprising an assist spring biasingsaid first member after the first member moves away from an uprightposition.
 16. The chair according to claim 15 wherein said assist springis compressed as said first member moves between an intermediateposition and a reclined position.
 17. The chair according to claim 16wherein said assist spring is compressed between said third member andsaid fourth member.
 18. The chair according to claim 4 furthercomprising a main spring biasing said first member from a rearwardposition to a forward position, a stop restricting forward movement ofsaid first member, and an assist spring biasing said first member fromsaid rearward position to an intermediate position.
 19. The chairaccording to claim 18 wherein said first member comprises a yoke, saidsecond member comprises a seat support, said third member comprises abase, said fourth member comprises a bearing guide, said main spring iscompressed between a rear spring guide and a front spring guide whensaid yoke moves rearward, said front spring guide is attached to saidbearing guide, said stop is fixedly attached to said yoke, said stopabuts against a top side of a stop slot formed into said base therebyrestricting forward movement of said yoke and said stop abuts against abottom side of said stop slot thereby restricting rearward movement ofthe yoke, and said assist spring is compressed between said base andsaid bearing guide when said yoke moves between an intermediate positionand a reclined position.
 20. A chair comprising: a main spring biasing aback from a reclined position to an upright position and an assistspring biasing said back from said reclined position to an intermediateposition.
 21. The chair according to claim 20 wherein said assist springis compressed between a non-moving face and a moving face thatcorrespondingly moves as said main spring moves.
 22. The chair accordingto claim 21 wherein said non-moving face defines a back face of a pocketformed into a base and said moving face defines a surface on a bearingguide slidably received in said pocket.
 23. The chair according to claim22 further comprising a spring guide compressing one end of said mainspring, wherein said spring guide is fixedly attached to said bearingguide so that said corresponding movement between said moving face andsaid main spring is coextensive.
 24. The chair according to claim 23further comprising a mount attached to said moving face, wherein saidassist spring is attached to said mount.
 25. The chair according toclaim 24 wherein said mount comprises an outer diameter that fits snuglywithin an inner diameter of said assist spring, a ramped tab within saidouter diameter, and an undercut area below said ramped tab; said assistspring comprises a bent inward end that is received by said undercutarea thereby locking the assist spring onto the mount.
 26. The chairaccording to claim 20 wherein said assist spring is attached to a mount;said mount comprises an outer diameter that fits snugly within an innerdiameter of said assist spring, a ramped tab within said outer diameter,an undercut area below said ramped tab; said assist spring comprises abent inward end that is received by said undercut area thereby lockingthe assist spring onto the mount.
 27. A chair comprising: a seat a chairstem assembly attached to a bottom of said seat, a cylinder installedwithin said chair stem assembly comprising a valve pin moveable fromside-to-side, and an actuating member having an interior cavity whereinsaid valve pin is received into said interior cavity.
 28. The chairaccording to claim 27 further comprising an actuating stem engaging saidactuating member.
 29. The chair according to claim 28 wherein saidinterior cavity comprises a funnel-like interior cavity, said actuatingmember comprises a slot along an end of the actuating member opposite ofsaid funnel-like interior cavity, said actuating stem comprises asmaller diameter nose and a larger diameter shoulder along one end ofthe actuating stem wherein the smaller diameter nose is received withinsaid slot and said larger diameter shoulder abuts a side surface of theactuating member.
 30. The chair according to claim 29 wherein saidactuating member comprises a funnel-like exterior surface along the sameend as said funnel-like interior cavity.
 31. The chair according toclaim 30 wherein said funnel-like exterior surface comprises an outerdiameter that is approximately the size of an inner diameter of saidchair stem assembly, wherein said outer diameter of said actuatingmember abuts against said inner diameter of said chair stem assemblywhen said actuating stem engages the actuating member thereby forcingsaid valve pin to the side.
 32. The chair according to claim 31 whereinsaid slot is positioned along a top of side of said actuating member andsaid funnel-like interior cavity and said exterior funnel-like surfaceare positioned along a bottom side of said actuating member.
 33. Thechair according to claim 32 wherein said actuating stem is disposedthrough a pressure adjustment knob, said actuating stem comprises abutton that can be depressed by a user thereby engaging said actuatingmember, and said slot comprises a snap that retains said actuating stem.34. The chair according to claim 27 wherein said actuating membercomprises a funnel-like exterior surface along the same end as saidinterior cavity, said funnel-like exterior surface comprises an outerdiameter that is approximately the size of an inner surface of saidchair stem assembly, and said outer diameter of said actuating memberabuts against said inner surface of said chair stem assembly when saidactuating member is engaged thereby forcing said valve pin to the side.